According to preliminary results of a study by scientists at Exeter University, an area of the brain associated with being in a calm, meditative state lit up when people were shown pictures of rural settings.

But images of urban environments resulted in a significant delay in reaction, before a part of the brain involved in processing visual complexity swung into action as the viewer tried to work out what they were seeing.

The study, which used an MRI scanner to monitor brain activity, adds to a growing body of evidence that natural environments are good for humans, affecting mental and physical health and even levels of aggression.

Dr Ian Frampton, an Exeter University psychologist, stressed the researchers still had more work to do, but said they may have hit upon something significant.

"When looking at urban environments the brain is doing a lot of processing because it doesn't know what this environment is," he said. "The brain doesn't have an immediate natural response to it, so it has to get busy. Part of the brain that deals with visual complexity lights up: 'What is this that I'm looking at?' Even if you have lived in a city all your life, it seems your brain doesn't quite know what to do with this information and has to do visual processing," he said.

Rural images produced a "much quieter" response in a "completely different part of the brain", he added.

"There's much less activity. It seems to be in the limbic system, a much older, evolutionarily, part of the brain that we share with monkeys and primates."

BEAUTIFUL

The effect does not appear to be aesthetic as it was found even when beautiful urban and "very dull" pictures of the countryside were used.

Prof Michael Depledge of Exeter University, a former chief scientist at Britain's Environment Agency, said urban dwellers could be suffering in the same way as animals kept in captivity.

He said the move to the cities had been accompanied by an "incredible rise in depression and behavioural abnormalities".